Orion MAK-500 vs C90 spotter for casual astronomy use?

[Thomas Morris]

I sent this same question to the folks at Orion (Telescope and
Binocular center), but thought I'd also rely on the collected
net-wisdom on this question:

A quick (and probably stupid) question. In both the online
catalog and the printed Orion (Telescope and Binocular Center)
catalog, preference is given to the Celestron C90 (versus the MAK-500)
for casual astronomy use.

Why is this? Differences in the coatings? Color aberrations?

I'm looking for an ultraportable, reasonably low-cost
spotting-scope type of thing, which could be used for
photography, and for occassional, casual astronomy.

Yes, I -know- that aperature is important, and that for
astronomy use, for not a whole lot more than the cost of
either of these, I could have something like a shorttube
80 or firstcope 80, or even a 6" or 8" dob newt. But I don't
think I would consider a 6" or 8" dob newt to be "ultraportable."
Much better for astronomy use, yes.

I'd think that with the shorter focal length (f 5.6) of the
MAK-500, this should give a wider field of view than the
f10 or f11 of the C90.

Thanks in advance!
Tom Morris
tom-m...@mindspring.com

[Akkana Peck]

Tom Morris <tom-m...@mindspring.com> wrote:
>>catalog, preference is given to the Celestron C90 (versus the MAK-500)
>>for casual astronomy use.
>>
>>Why is this? Differences in the coatings? Color aberrations?
>

>The very nice response I got from the folks at Telescope and
>Binoc center was that since the MAK-500 has a shorter focal
>length (?f5.6) than that of the C90 (f11?), the size of the secondary
>in the MAK-500 is larger than that in the C90.
[ ... ]
>that the MAK-500 might have 10-20% less effective aperature.

That's part of it. Another reason may be that faster optics tend
to give worse images because they're harder to figure accurately
and they're more sensitive to collimation problems.

I have a Pro-Optic 500 f/5.6 Mak, which as far as I can tell is the
same unit as the Orion MAK-500 with different paint. A friend has
a C90, and we set up a comparison once at Fremont Peak. On the
Orion nebula, the C90 gave significantly better star images.
The f/5.6 showed as much nebulosity but showed a lot of coma in
the images of the stars, which got worse at higher magnification.

Unfortunately, the fog rolled in before we could try any other targets
(we were hoping to compare planetary images) and we haven't had a chance
to continue the test. Maybe sometime soon.

I should mention that I was using my Pro-Optic with the 45-degree
erecting prism diagonal that came with it, whereas the C90 was using
a real star diagonal. It's possible that some of the optical problems
were due to the chintzy diagonal. I recently bought a 90-degree
mirror diagonal (figuring that at f/5.6 the difference between a
prism and a mirror might be significant) and hope to do a comparison
between the two diagonals tonight.

Also, I suspect that better collimation might help the Mak's images
a lot. I haven't yet worked up the nerve to try to collimate it. :-)

The f/5.6 isn't a bad ultraportable -- I have a mini-review of it at
http://www.best.com/pro-optic500.html. It gives reasonable wide-field
views, especially given its extremely small size, light weight and low
cost, and it's a decent telephoto lens (I use it quite a bit for
wildlife and lunar photography). Doesn't do anything exceptionally
well but does a lot of things decently. I don't regret buying mine
(but wouldn't want it -- nor a C90 -- as my only telescope!)

...Akkana http://www.best.com/~akkana/astro.html

[Tom Morris]

tom-m...@mindspring.com (Thomas Morris) wrote:

>A quick (and probably stupid) question. In both the online
>catalog and the printed Orion (Telescope and Binocular Center)

>catalog, preference is given to the Celestron C90 (versus the MAK-500)
>for casual astronomy use.
>
>Why is this? Differences in the coatings? Color aberrations?
>

The very nice response I got from the folks at Telescope and
Binoc center was that since the MAK-500 has a shorter focal
length (?f5.6) than that of the C90 (f11?), the size of the secondary
in the MAK-500 is larger than that in the C90.

You can actually see this in the pictures of the MAK-500 and C90
in the catalog or on the www.oriontel.com web pages.

So the MAK-500 has more obstruction in its field of view than the
C90. I guess this means that although both of these are 90mm
scopes, that the MAK-500 might have 10-20% less effective aperature.

Tom Morris
tom-m...@mindspring.com.x-nospam-here (take off from .x on!)